1. Field of the Invention
The present invention relates to a lens driving device, in particular to a lens driving device with plate springs for elastically supporting a lens support for retaining a lens.
2. Description of Related Art
In recent years, in mobile telephones, a camera mounted in a smartphone (multifunctional mobile telephone) or a tablet device not only has high pixel but also mostly includes an auto focus device. As shown in FIG. 16, as a lens driving manner with the auto focus device, the lens driving device using a voice coil motor is widely adopted.
As shown in FIG. 16 to FIG. 21, the lens driving device using the voice coil motor includes a lens support 3, a driving coil 4, a lower spring 2, an upper spring 7, a square magnet yoke 9 and a plurality of magnets 6. The central part of the lens support 3 forms a thread part 3d for retaining the lens (unshown in figures). The driving coil 4 is mounted on the lens support 3. The lower spring 2 and the upper spring 7 are respectively mounted on the lens support 3 and are used for supporting the lens support 3 from the lower side and the upper side. The square magnet yoke 9 is mounted around the lens support 3, and is composed of magnetic substances such as soft iron serving as an outer side metal cover. The magnets 6 are mounted on the magnet yoke 9, and the outer circumferences of the magnets 6 are shaped to conform (cooperate) to the shape of the inner wall of the magnet yoke 9, and the inner circumferences of the magnets 6 are shaped to cooperate to the shape of the outer circumference of the driving coil 4.
An outline part 2d of the lower spring 2 is shaped to be corresponding to a plate spring outline retaining part 1d of a lower side fixing body 1, and the lower spring 2 is mounted on the lower side fixing body 1. An outline part 7d of the upper spring 7 is shaped to be corresponding to a plate spring outline retaining part 8d of an upper side fixing body 8 mounted on the magnet yoke 9, and the upper spring 7 is mounted on the upper side fixing body 8. An inner ring part 7e of the upper spring 7 is shaped to be cooperating to the upper surface of the lens support 3.
A plurality of guiding parts 1b are arranged at the four corners of the lower side fixing body 1. The guiding parts 1b abut against a plurality of guiding parts 8b at the four corners of the upper side fixing body 8, and thus the height of the lens driving device is determined.
The driving coil 4 is arranged in a magnetic field generated by the magnet yoke 9 and the magnets 6 and distributed around the driving coil 4 radially. Therefore, an arrow as shown in FIG. 17, with the driving coil 4 is electrified, the driving coil 4 generates a Lorentz force towards the directions extending along a object to be shot (upper direction and lower direction). Under the action of the Lorentz force, the driving coil 4 moves the lens support 3 to a preset position balanced with restoring force of the lower spring 2 and the upper spring 7.
Therefore, the lens driving device as shown in FIG. 16 controls the amount of movement of the lens support 3 by adjusting the amount of current flowing into the driving coil 4, thus the position of the lens (unshown in figures) can be controlled freely.
Moreover, as shown in FIG. 16 to FIG. 19, a plurality of guiding parts 7a of the upper spring 7 are engaged with a plurality of front end clamping parts 3a of the lens support 3 so as to determine the rotation direction of the lens support 3. A plurality of bending parts 9a are arranged in the magnet yoke 9 and are taken as clamping mechanisms for limiting the amounts of movement in the vertical direction. The bending parts 9a are inserted between the recessed outside wall part (clamping part in the side face direction) 3e of the lens support 3 and the inner side of the driving coil 4. A plurality of clamping parts 3f are arranged near the lower side mounting position of the driving coil 4, namely the inner side of the driving coil 4.
The clamping parts 3f of the lens support 3 control the amount of movement of the lens by utilizing lower end faces 9c of the magnet yoke 9. The lower end faces 9c of the magnet yoke 9 and the clamping parts 3f of the lens support 3 are partitioned at an interval C when the magnet yoke 9 is not driven, and the magnet yoke 9 abuts against the clamping parts 3f of the lens support 3 when the magnet yoke 9 is driven. That is to say, when the magnet yoke 9 is driven, a plurality of the side faces 9b are used for limiting the interval C as the maximum amount of movement to be zero, and so as to prevent the lens driving device from moving.
In addition, in recent years, with the development of high pixelate of the cameras, in order to solve the problems such as the lens driving device is influenced by falling impact and the characteristics of the lens driving device cannot be functioned, a solution that adding a clamping mechanism to the lens driving device for limiting the amount of movement in the plane direction or the rotation direction is proposed.
For example, as shown in FIG. 16 and FIG. 20, the bending pats 9a of the magnet yoke 9 formed by base materials such as high-strength soft iron are used as the clamping mechanisms in the plane direction. Specifically, when the lens driving device is not driven, the bending parts 9a formed in the inner circumference side of the magnet yoke 9 and extending towards the lower side and the recessed outside wall part (clamping part in the side face direction) 3e of the lens support 3 are mutually partitioned at an interval (maximum amount of movement) E. Moreover, when the lens driving device is driven the bending parts 9a and the recessed outside wall part 3e abut against together, and thus the movement in the plane direction is limited (the state that the interval E is zero is formed so that the lens driving device does not move).
In addition, the existing lens driving device also includes a clamping mechanism in the rotation device. The amount of movement in the rotation direction is limited by the clamping mechanism in the rotation direction, so that the spring components cannot be damaged under the effect of a large torque.
For example, when the lens driving device as shown in FIG. 16 and FIG. 21 is not driven, a maximum amount of rotation F in clockwise direction and in anticlockwise direction is formed between the side faces 9b in the bending parts 9a of the magnet yoke 9 and the guiding parts 3b of the lens support 3 extending towards the outer circumference side. Moreover, with the driving of the lens driving device, the side faces 9b of the magnet yoke 9 abut against a plurality of clamping parts 3c of the lens support 3. The spring components are limited to the maximum amount of rotation F, so that micro deformation such as extending or bending cannot occur in the spring components under the effect of rotation torque generated when the lens is screwed in.
In order to prevent hysteresis caused by mutual contact among components of the lens driving device using the voice coil motor, the upper spring 7 and the lower spring 2 are utilized for connecting the upper part and the lower part of the lens support 3. Thus, after the lens support 3 moves and begins to float, before the lens support 3 moves the interval (maximum amount of movement) C, the interval between the lens support 3 and all components is retained, and the lens support 3 is not in contact with other components.
However, under the condition that the impact in the vertical direction is applied to the lens driving device due to falling, the clamping parts 3f of the lens support 3 as the clamping mechanism in the vertical direction sometimes collide with the lower end faces 9c of the magnet yoke 9, the clamping parts 3f are damaged, or the driving coil 4 is fallen off by the impact, or the impact is transferred to the connected lower spring 2 or upper spring 7 and the lower spring 2 or the upper spring 7 generates micro deformation, and thus the characteristics and functions of the lens driving device cannot be developed.
In addition, under the impact in the plane direction, the recessed outside wall part 3e of the lens support 3 as the clamping mechanism in the plane direction sometimes collides with the bending parts 9a of the magnet yoke 9, which may cause stress of the recessed outside wall part 3e, damage to welds as resin jointing parts and falling of the driving coil 4, or micro deformation of the connected lower spring 2 or upper spring 7 for the impact is transferred to the connected lower spring 2 or upper spring 7, and thus the effects of characteristics and functions of the lens driving device cannot be developed.
And then, the condition that the lens support 3 rotates sharply in the direction of the falling impact further appears. For example, under the condition that the impact in the rotation direction is applied, the clamping parts 3c of the lens support 3 as the clamping mechanism in the rotation direction collide with the side faces 9b of the magnet yoke 9 when the lens is screwed in, the clamping parts 3c are damaged by pressing or grinding, and thus the impact is transferred to the connected lower spring 2 or upper spring 7 to generate micro deformation, or garbage is generated at the interior and falls to the inside of the lens driving device, so that characteristics and functions of the lens driving device cannot be developed.
A method for alleviating the impact in the vertical direction applied on the lens driving device is disclosed in Patent Literature 1 (JP 2006-251728), and a plurality of elastic projections are arranged near a plurality of clamping parts 8a of the upper side fixing body 8. The projections are made of common liquid crystal polymer used in the lens driving device. And in order to obtain sufficient elastic force, sufficient length of the lens driving device needs to be ensured. However, under the condition that the size of the lens driving device in the vertical direction is kept shorter, the thickness is thinned and the elastic force is obtained, and problems exist in the view of strength or deformation. In order to enable the projections arranged on the lens driving device in the patent literature to obtain sufficient elastic force, the size of the lens driving device needs to be prolonged along the vertical direction.
And then, as disclosed in the Patent Literature 1, in order to shelter from the garbage, almost all lens driving devices are formed into the structures that the magnet yoke 9 is disposed on the outermost side, but a compact shock absorber structure is difficult to mount on the inside of the magnet yoke 9.
In addition, in order to adapt for the high pixel, the lens driving device uses a lens with larger lens diameter compared with a former lens driving device or increase the piece number of lens of a laminated lens with increased (for example, former three lenses are increased to four lenses, or former four lenses are increased to five lenses). Therefore, the weight of the laminated lens is increased with the increase of the piece number of lenses or the enlargement of the lens diameter, and the weight of the lens driving device is also increased, and thus the impact to the lens driving device is also increased. In order to cope with the increased impact force along with the increase of weight, the thickness of the clamping part 8a as the clamping mechanism in the vertical direction or the recessed outside wall part 3e of the lens support 3 as the clamping mechanism in the plane direction is increased so as to improve the strength, or the thickness of the bending parts 9a is increased so as to increase the contact area between the clamping parts 3c of the lens support 3 as the clamping mechanism in the rotation direction and the side faces 9b of the magnet yoke 9, and thus barrier to miniaturization of the lens driving device is reduced.
Moreover, under the condition that a large lens which is larger than former lens is used and the sizes of the magnets 6 are not reduced, the lens is difficult to be assembled in the shape which is the same as the existing shape structurally, and the bending parts 9a of the magnet 9 are difficult to be inserted between the recessed outside wall part 3e of the lens support 3 and the driving coil 4. Therefore, a structure that the bending parts 9a of the magnet 9 do not need to be inserted between the recessed outside wall part 3e and the driving coil 4 is disclosed (referring to Patent Literature 2: JP 4966750).
FIG. 22 to FIG. 25 are perspective views of a lens driving device using a large lens. Moreover, with reference to FIG. 16 to FIG. 21, the same components in FIG. 22 to FIG. 25 are referenced by identical reference numbers, and description of the identical reference numbers is omitted.
As shown in FIG. 22 to FIG. 25, in the lens driving device using a large lens, the intervals between the front end clamping parts 3a of the lens support 3 and the clamping parts 8a of the upper side fixing body 8 are set to be the maximum amounts of movement C, and the front end clamping parts 3a and the clamping parts 8a are utilized for limiting the lens support in the vertical direction.
The limitation in the plane direction is carried out by utilizing a cylindrical dividing wall if disposed at the central part of the lower side fixing body 1 and a flange part 3k disposed at the central part of the lens support 3 on the side opposite to the side of the object to be shot. The interval between the dividing wall 1f and the flange part 3k is set to be the maximum amount of movement E.
The limitation in the rotation direction is carried out by utilizing a plurality of clamping parts 1g arranged on the outside of the dividing wall 1f of the lower side fixing body 1 and a plurality of groove parts 2m arranged on the outside of the flange part 3k of the lens support 3. The intervals between the clamping parts 1g and the groove parts 3m are set to be the maximum amounts of rotation F. By utilizing the formed lens driving device, the amount of movement in the vertical direction, the amount of movement in the plane direction and the amount of rotation in the rotation direction of the lens support can be limited.
In addition, suppose the lens driving device mounted in the smart phone has various using methods (for example, the main body of the smart phone can be beat or swung repeatedly during the playing of games), and thus durability for resisting impact generated by low falling at the height of 5 cm to 15 cm (the falling relative to about 1.6 m is usually called low falling) in thousands to tens of thousands times is needed. In the existing lens driving device, the clamping parts of the clamping mechanisms in the vertical direction, the plane direction and the rotation direction are damaged slowly under the effect of impact, or micro deformation of the spring component occurs repeatedly under the effect of repeated impact force, and thus degradation easily occurs. Therefore, in the current lens driving device, countermeasures which do not interference with miniaturization and can improve the durability of the components for the repeated impact resistance needs to be researched.